New dissertation about impact of lignin on microbial metabolism in colon

29.4.2016 16:00

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Lignin,
part of the cell wall in plants, is a fascinating research area, for
which VTT is developing new practical applications. One interesting
possibility would be to use lignin in food applications. Based on a
doctoral dissertation by VTT's Research Scientist Piritta Niemi colon
microbiota can partially metabolise lignin. Her research also suggests
that even a high lignin content in dietary fibre does not prevent colon
microbiota from playing its important role of converting carbohydrates
into short chain fatty acids.

The importance of lignin in digestion not well known

Very little research has
been done on the importance of lignin in digestion. It has been
generally assumed that lignin is not metabolised during digestion and
that it has no significant benefits or disadvantages in this regard.
However, there are also studies suggesting that colon microbiota can
metabolise at least part of lignin into various kinds of metabolites,
which may be bioactive. These include intestinal enterolignans, for
example.

Lignin-rich fractions from BSG were studied

In Piritta Niemi's doctoral dissertation, lignin-rich
fractions were enzymatically fractionated from BSG (Brewers' Spent
Grain), and the fractions were used to investigate the interactions
between lignin and colon microbiota in an in vitro metabolic
colon model. The microbiota formed several phenolic metabolites from the
lignin-rich fractions and these metabolites were most likely derived
from lignin. According to these results colon microbiota can at least
partially metabolise lignin.

The dissertation also examined
whether high lignin content suppresses the microbial conversion of
carbohydrates, or the growth of Lactobacillus and Bifidobacterium
bacteria which are generally considered to be beneficial. Colon
microbiota can metabolise carbohydrates in dietary fibre into sugars,
which is used as an energy source by fermenting them to short chain
fatty acids. Short chain fatty acids are beneficial to humans, which is
why it is important that lignin does not suppress their formation. In
the colon model study no signs of suppression of microbial carbohydrate
conversion by a high lignin-content (20–40%) in fibre were detected.
Neither did a lignin-rich growth substrate inhibit the growth of Lactobacillus and Bifidobacterium bacteria.

More
than 30 million tons of BSG are produced in the world every year as a
by-product of the brewery sector. BSG, which is food grade material, is
mainly used as a feed additive for ruminants. In addition to dietary
fibre, it contains around 20% protein, which means that it could be put
to more valuable use than in feed – for example in food applications.

Bioactivities of lignin metabolites yet to be studied

With
respect to lignin, in the future it will also be important to study the
bioactivities of the metabolites observed in Ms Niemi's dissertation
and whether they have potentially health-promoting effects. It is likely
that lignin has more importance as a constituent of dietary fibre than
has so far been realised.